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Nuclear reactions induced by charged particles are used to determine total carbon, nitrogen, and oxygen in atmospheric aerosols. The methods are nondestructive of the sample, permitting the same sample to be studied by other experiments such as x-ray photoelectron spectroscopy. The 109.8-minute 18 F was followed by its 0.511 MeV annihilation radiation.The second method uses a proton beam to induce the 16 o(p,a) 13 N reaction.The two methods were used to check one another. A comparison of the oxygen found in ten samples by 3 He activation analysis with that found by proton activation analysis shows an average percent difference of 18%,The sensitivity for detection of oxygen is approximately 5 ~g/cm 2 and is primarily limited by the rather large oxygen blank in the silver filter. CONTENTS

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